thestarfandomcom-20200214-history
Altair,Procyon Binary Stars,Vega,Regulus Binary Stars and Alpha Virginis Binary Stars
Altair (Alpha Aquilae, Alpha Aql, αAquilae, αAql, Atair) is the brightest star in the constellation Aquila and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitudeof 0.77 and is one of the vertices of the Summer Triangle; the other two areDeneb and Vega.[2][7][9] Altair rotates rapidly, with a velocity at the equator of approximately 286 km/s.[nb 3][4] A study with the Palomar Testbed Interferometerrevealed that Altair is not spherical, but is flattened at the poles due to its high rate of rotation.[10] Other interferometric studies with multiple telescopes, operating in the infrared, have imaged and confirmed this phenomenon.[4] Procyon (α CMi, α Canis Minoris, Alpha Canis Minoris) is the brighteststar in the constellation Canis Minor. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visualapparent magnitude of 0.34.[3] It is actually a binary star system, consisting of a white main sequence star of spectral type F5 IV-V, named Procyon A, and a faint white dwarf companion of spectral type DA, named Procyon B. The reason for its brightness is not its intrinsic luminosity but its closeness to the Sun; as determined by theHipparcos astrometry satellite,[1][8] it lies at a distance of just 11.46light-years (3.51 parsecs),[2] and is therefore one of our nearest stellar neighbours. Its closest neighbour is Luyten's Star, about 1.12 ly (0.34 pc) away, and the latter would appear as a visual magnitude −7 star in the night sky of a hypothetical planet orbiting Procyon.[9]Procyon forms one of the three vertices of the Winter Triangle, along with Sirius and Betelgeuse. Vega (α Lyr, α Lyrae, Alpha Lyrae) is the brightest star in theconstellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun's neighborhood. Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun."[12] Vega was the northern pole star around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14'.[13] Vega was the first star other than the Sun to be photographed and the first to have itsspectrum recorded. It was one of the first stars whose distance was estimated through parallax measurements. Vega has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV photometric system. Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their life expectancies. Vega has an unusually low abundance of the elements with a higheratomic number than that of helium.[8] Vega is also a suspected variable star that may vary slightly in magnitude in a periodic manner.[14] It isrotating rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photospherethat reaches a maximum at the poles. From Earth, Vega is being observed from the direction of one of these poles.[9] Based on an observed excess emission of infrared radiation, Vega appears to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk, which is analogous to the Kuiper belt in the Solar System.[15] Stars that display an infrared excess because of dust emission are termed Vega-like stars.[16]Irregularities in Vega's disk also suggest the presence of at least one planet, likely to be about the size of Jupiter,[17] in orbit around Vega.[18] Regulus (α Leo, α Leonis, Alpha Leonis) is the brightest star in theconstellation Leo and one of the brightest stars in the night sky, lying approximately 77.5 light years from Earth. Regulus is a multiple starsystem composed of four stars that are organized into two pairs. Thespectroscopic binary Regulus A consists of a blue-white main-sequencestar and its companion, which has not yet been directly observed, but is probably a white dwarf star.[4] Located farther away is the pair Regulus B and Regulus C, which are dim main-sequence stars. Spica (α Vir, α Virginis, Alpha Virginis) is the brightest star in theconstellation Virgo, and the 15th brightest star in the nighttime sky. It is 260 light years distant from Earth. A blue giant, it is a variable of the Beta Cephei type.